In this proposal, we will study the Jaagsiekte Sheep Retrovirus (JSRV) that induces ovine pulmonary carcinoma (PC) in sheep. OPC is an infectious neoplasm of sheep that occurs in many geographical locations. It is analogous to human brochiolar aveolar carcinoma (BAC) that accounts for approximately 25% of lung cancer in humans. OPC and BAC are neoplasms of secretory type II pneumocytes (that make pulmonary surfactants) and Clara cells. Previous experiments by others have made a strong case that the etiologic agent of PC is a type D retrovirus (JSRV). The genome organization of JSRV has been deduced from a series of cDNA clones isolated from the lung fluid of a sheep with OPC. However, the previous JSRV clone was not infectious. In preliminary experiments, we have isolated a complete JSRV pro-virus from a field isolate of OPC, JSRV-21. Direct, intratracheal injection of JSRV-21 DNA into newborn lambs resulted in infection, as detected by hemi-nested PCR of PBMCs, lymph nodes and lung tissue. We also have been able to generate substantial quantities of JSRV virus by transfection of modified JSRV-21 plasmids into human 293T cells. These and related regents allow a focused study on the molecular and oncogenic properties of JSRV. In this proposal, we will carry out the following experiments: 1) Identification of an oncogenic clone of JSRV; 2) Molecular characterization of JSRV; 3) Development of an in vitro culture system for JSRV; and 4) Investigation of the role of orf-X in JSRV infectivity and oncogenicity. These experiments will provide insight into JSRV-induced lung cancer in sheep, and possibly into human BAC.